COD reduction has been under study for many years. The subject is of considerable practical interest because of the importance of effluent pollution.
From patent application JP/58006286-A it is known to use humic acids of various origin as flocculating agents for removing pollutants present in certain types of effluent.
In said patent application COD reduction is obtained by using these acids together, however, with inorganic flocculating agents (in particular a solution of a polyvalent metal such as FeCl.sub.3), operating with a final pH of between 6 and 7.
It has now been found that if said acids are used under particular operating conditions there is no need for the presence of inorganic flocculating agents as used in the method of the cited Japanese application.
Humic acids are a heterogeneous class of macromolecular organic acids which form when plant constitiuents (lignin etc.) are decomposed by micro-organisms under aerobic conditions; they can either be extracted from soils, lignites etc. or be prepared from coal by oxidative degradation using various oxidants (O.sub.2, KMnO.sub.4, HNO.sub.3 etc.).
In the second case the humic acids are defined as "regenerated", and although they probably differ structurally from those of natural origin they have a marked resemblance to them in terms of their elemental composition, properties and functional groups.